Energy harvesting is a key development in the deployment of self-sustaining systems. Energy harvesting is the process of deriving, capturing, and utilizing energy from a system environment, rather than a power source, such as a battery or traditional power supply. Some of the most popular energy harvesting schemes include piezoelectric crystals (i.e., generating a small voltage when the crystal is mechanically deformed during vibration), photovoltaic cells (i.e., converting solar energy into voltage), thermoelectric generators (i.e., producing a voltage from a temperature gradient), and inductive coupling (i.e., making use of specialized antennae to capture the energy contained in electromagnetic fields). Electronics implemented and powered solely using these methods are often self-sustaining, requiring no additional power source.
In many instances, energy harvesting is used to provide a small amount of power for low-energy electronics. While the energy to power some large-scale electronics from oil and coal resources is costly, the source of energy used in energy harvesting devices is generally present as ambient background, and is therefore free. For example, piezoelectric energy harvesting systems in bridges can be powered by vibrations in the structure caused by traffic and used for structural health monitoring.